It would be interesting to also include the model year of Focus, since it seems at least that those with '13 Foci aren't having as many problems.

I don't know about that, it appears by most accounts that both the '12s and '13s have the same hardware and software (provided the '12s have been updated properly). It's probably just that the '13s haven't been out as long; sometimes the DCT quirks take time to manifest.